rhashtable currently only does bh-safe synchronization making it impossible
to use from irq-safe contexts. Switch it to use irq-safe synchronization to
remove the restriction.

v2: Update the lock functions to return the ulong flags value and unlock
    functions to take the value directly instead of passing around the
    pointer. Suggested by Linus.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reviewed-by: NDavid Vernet <dvernet@meta.com>
Acked-by: NJosh Don <joshdon@google.com>
Acked-by: NHao Luo <haoluo@google.com>
Acked-by: NBarret Rhoden <brho@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>